1. Field of the Invention
The present invention relates to a battery system using non-aqueous secondary batteries typically represented by lithium ion batteries, a battery device having the battery system mounted thereon, and a battery system-mounted vehicle.
2. Description of the Related Art
In recent years, lithium ion batteries have been utilized as a driving power supply for vehicles such as hybrid cars and electric cars and portable electronic devices such as notebook personal computers and digital cameras.
Degradation phenomena occur in such a battery system using lithium ion batteries. Due to repeated charge-discharge cycles, the battery capacity is lowered and the direct current resistance of the battery is increased, resulting in degradation phenomena. The degradation phenomena likely occur in charge-discharge cycles under the condition of large current and large capacity. For example, the degradation phenomena means that the capacity of insertable lithium ions to positive or negative electrode materials decreases and thereby battery performance lowers. Therefore, charging or discharging to a lithium ion battery is controlled such that the state of charge (SOC) of the battery falls within a predetermined range. Japanese Patent No. 4052080 discloses a control device that judges the state as overcharge when the voltage of a lithium ion battery exceeds a maximum allowable voltage and judges the state as over-discharge when the voltage is lower than the minimum allowable voltage, thereby stopping charging or discharging.